Dielectric properties of anodic films formed on sputtering-deposited tantalum in phosphoric acid solution

The dielectric properties of anodic films formed on tantalum in dilute phosphoric acid solution, at 20 and 85 °C, have been investigated by electrochemical impedance spectroscopy. Dielectric constants of 28.2±0.9 (20 °C) and 30.2±2.1 (85 °C) were determined from the slopes of the variations of reciprocal capacitance of the anodic film and of film thickness, from transmission electron microscopy, with formation voltage. The slightly higher dielectric constant obtained at 85 °C is due to a reduced amount of incorporated phosphorus species in the outer layer of anodic films formed at this temperature, together with a reduced thickness of the outer layer, compared with those of anodic films formed at 20 °C.